Chlorofluorocarbons (CFCs) (i.e., compounds that contain only carbon, chlorine and fluorine atoms) are used in a variety of applications, although use of these materials is declining due to environmental regulations stemming from their role in the depletion of stratospheric ozone. Nonetheless, they remain useful chemical intermediates. In particular, they can function as precursors to hydrofluorocarbons (HFCs) (i.e., compounds that contain only hydrogen, fluorine and carbon atoms) and hydrochlorofluorocarbons (HCFCs) (i.e., compounds that contain only hydrogen, fluorine, chlorine and carbon atoms) which can be used in place of CFCs in many cases. HFCs are not believed to contribute to ozone depletion and HCFCs are believed to contribute less than CFCs to ozone depletion. Although useful HFCs and HCFCs have been found, the search continues for other useful HFCs and HCFCs (particularly those having at least four carbon atoms) and improved methods for making HFCs and HCFCs.
One area in which there has been limited exploration concerns compounds that have a --CCl.sub.2 CCl.sub.2 -- radical. Compounds having a --CC1.sub.2 CC1.sub.2 -- group are generally prepared by the chlorination of a suitable unsaturated material such as an alkyne or a vicinal dichloroalkene (e.g., --CC1.dbd.CC1--). For example, 2,2,3,3-tetrachloroperfluorobutane (i.e., CF.sub.3 CC1.sub.2 CC1.sub.2 CF.sub.3) can be prepared by the chlorination of 2,3-dichloro-hexafluoro-2-butene (i.e., CF.sub.3 CC1.dbd.CC1CF.sub.3) or hexafluoro-2-butyne and 2,2,3,3-tetrachloroperfluoropentane (i.e., CF.sub.3 CCl.sub.2 CCl.sub.2 CF.sub.2 CF.sub.3) can be prepared by the chlorination of CF.sub.3 C.tbd.CCF.sub.2 CF.sub.3 (see Miller et al., 83 Journal Amer. Chem. Soc. 1767 (1961)). Alternatively, depending on the remainder of the molecule, they may be prepared by chlorination of a saturated compound having a --CH.sub.2 CH.sub.2 -- group. Such processes are of little utility when the --CC1.sub.2 CC1.sub.2 -- compound is to be employed as the precursor to an HFC, since the reduction of its precursor (e.g. an alkyne) serves to provide the HFC. In other words, in order to obtain the desired HFC, the starting material for producing the --CCl.sub. 2 CCl.sub.2 -- compound must include the same number of carbon atoms as the desired HFC and the unsaturated bond must be in the correct position. A need exists, therefore, for an improved method of preparing CFCs containing a --CC1.sub.2 CC1.sub.2 -- group, and for novel CFCs that contain a --CCl.sub.2 CCl.sub.2 -- group which may be useful as intermediates for producing HFCs.
Alternative methods have been mentioned in the literature, but they do not appear practical primarily because of the low yields of the desired --CCl.sub.2 CCl.sub.2 -- containing compound.
For example, U.S. Pat. No. 2,644,835 to U.S. Rubber describes a generic structure of RCC1.sub.2 CC1.sub.2 R', wherein R and R' each contain a chain of at least two carbon atoms and R may be substituted with a list of radicals, fluorine being among them. Although fluorine is mentioned as a possible substituent, no CFCs are listed among the specifically identified compounds. The RCC1.sub.2 CC1.sub.2 R' compounds were prepared by the reduction of reactants having a structure of RCC1.sub.3 and R'CCl.sub.3 in the presence of a catalyst, such as PtO.sub.2, and a base, such as alcoholic ammonia.
Vapor phase thermal chlorination of CF.sub.3 CH.sub.x C1.sub.3-x wherein x is 1 to 3 over a solid catalyst to give CF.sub.3 CC1.sub.3 has recently been described, but no mention is made of products containing more than 2 carbons (see U.S. Pat. No. 5,120,883 to DuPont). In fact, the total of the reported two-carbon materials in the product mixture is nearly 100%. Similarly, the vapor phase chlorination of either CF.sub.3 CF.sub.2 CH.sub.3 or CF.sub.3 CF.sub.2 CH.sub.2 C1 gave three-carbon products totaling 100% of the product mixture (see Japanese Kokai Patent Publication No. 4-154734 to Asahi Glass).
Vapor phase photolysis of CF.sub.3 CC1.sub.3 to CF.sub.3 CC1.sub.2 CC1.sub.2 CF.sub.3 and chlorine has been reported (R. N. Haszeldine and F. Nyman, "Oxidation of Polyhalogeno-compounds. Part II. Photolysis and PhotoChemical Oxidation of Some Chlorofluoroethanes", Journal Amer. Chem. Soc., 387-396 (1959)), but a conversion of 54% was obtained only after a period of 36 days.
A need also exists for an improved method of obtaining HFCs which are particularly useful as solvents. Japanese Kokai Patent Publication No. 3-123743 to Asahi Glass lists various HFCs, including CF.sub.3 CF.sub.2 CH.sub.2 CH.sub.2 CF.sub.2 CF.sub.3, that are useful for degreasing and flux removal when used in a mixture that includes CClF.sub.2 CF.sub.2 CHClF and/or CF.sub.3 CF.sub.2 CHCl.sub.2 as a major component. Although CF.sub.3 CF.sub.2 CH.sub.2 CH.sub.2 CF.sub.2 CF.sub.3 is mentioned in the examples, there is no description of a method for synthesizing this compound.
1,1,1,3,3,3,-Hexafluorobutane, the reduction product of CF.sub.3 CC1.sub.2 CC1.sub.2 CF.sub.3, has been mentioned as a potential zero ODP blowing agent (W. M. Lamberts, Polyurethanes World Congress 1991, Sept. 24-26, 1991, p 734).